Questions to Ask Your Doctor about Cancer Screening

Drs. Lisa Schwartz and Steven Woloshin of the Dartmouth Institute for Health Policy discuss the benefits and harms of cancer screening and highlight popular misconceptions about cancer screening statistics.

Lollar: What questions should patients ask about the cancer screening tests their doctors may recommend? Dr. Steven Woloshin and Dr. Lisa Schwartz are co-directors of the Center for Medicine and the Media at the Dartmouth Institute for Health Policy and Clinical Practice. The two general internists work together on a number of projects aimed at improving how medical information is communicated and understood.

Woloshin: People often hear the terms relative risk and absolute risk when they’re talking about cancer screening, and it’s just important that they be clear about what these things mean. You might hear 20 percent reduction in your chance of dying from the cancer if you’re screened. That may sound very good, and you may want to go for screening, but the thing you need to know is, what does that 20 percent really correspond to in absolute terms? What’s the difference? And the only way to know that is to start, you have to know the starting point. So 20 percent lower than what? So for example, if you go to a store and there’s a sale. Let’s say there’s a tie, it costs $10. And then let’s say the sale’s 20 percent off. The sales price would be $8.

Lollar: Eight dollars. That’s an absolute difference of 2 dollars. But, says Woloshin, a 20 percent sale on a fancy car that costs $40,000 may be more meaningful to you, because now the absolute difference is $8,000. In both examples, the relative difference is 20 percent. But, in order to decide how important that 20 percent really is, you need to know the absolute difference. When it comes to whether a screening test reduces your risk of death in a meaningful way, you need to know what the absolute risk of death is to begin with. Is it large, like a $40,000 car? Or small, like a $10 tie?

Woloshin: I think it's really important that patients ask a few questions to decide whether it's really worth it to them. So the first question to ask is to get a sense of what's my chance of dying from this cancer if I don't get screened? And what's my chance of dying from this cancer if I do get screened? Those are the absolute risks that you need to know.

Then you have to decide is that difference big enough that it's meaningful to you? Because you have to also think about what are the downsides to screening. Because it's not just about benefits. Screening also has harms. There could be false alarms …. The test comes back, and it looks like it might be cancer, and you have to undergo some kind of subsequent testing, which can be invasive. It could be very anxious period until you find out that it really was just a false alarm. Or there can be overdiagnosis, which means that there can be cancers that are detected that would never have gone on to cause harm, but they're picked up by screening, and then people undergo unnecessary treatment. And that's a harder question, but it's important to ask the person offering you screening, what is the chance that I'll be overdiagnosed?

Lollar: Drs. Woloshin and Schwartz also point out that, contrary to conventional wisdom, statistics about 5-year-survival are irrelevant when it comes to knowing if a particular screening test actually lowers the risk of death.

Woloshin: When people hear about screening tests, sometimes they'll hear about how the test affects survival, 5-year-survival. And that's something that can be very confusing to people because screening tests will reduce, will improve 5-year-survival whether or not they actually change their chance of dying. Survival statistics in the context of screening are very deceptive, and the safest thing for people to do is to ignore them.

Schwartz: The other question that I would encourage patients to ask is just say, do we have gold-standard evidence to tell us that this screening test really works? And for a screening test to really work, what that means is that it has to, in a randomized trial, demonstrate that the chance of dying from that cancer is lower in people who were screened versus people who weren't.

And even for screening tests where we do have a demonstrated benefit, we’ve taken the tactic that we need to scare people as much as possible. I think that creates a paradox. By creating more fear, we really worry that that makes people feel less healthy and more vulnerable and less resilient as individuals. And if our goal is to improve health, then I think we have to be very careful about overstating the benefits of screening and the chance that something bad is going to happen to you.

Woloshin: So I think it’s really important to inform patients as opposed to persuade them. Because in the end it’s the patients who … can get the benefit of screening but are also the ones who can suffer from the harms.

Schwartz: Some people will feel that they want to do everything that they can to lower their chance of dying from cancer. And you know they understand the harms but they just, they aren't nearly as important to them as the feeling that they've done everything that they can. And then there's other people who feel that I'm healthy right now and that this really to me seems like a tossup, and I don't want to do it. And I think what we want to do as physicians is help people to realize that you can make a good decision to be screened, and you can make a good decision not to be screened.

Posted: November
27, 2012

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